Alcohol-related sexual violence is a pervasive public health problem, with more than half of all sexual assaults occurring in the context of alcohol consumption (Abbey et al., 2004; Cleer & Lynn, 2013). Despite evidence that bystanders could play a critical role in preventing sexual assaults; no study has examined the role of bystander intoxication in intervening in a sexual assault. Guided by theory and empirical work, the Specific Aims of the proposed research involve testing the role of bystander intoxication at different steps of Latane and Darley's (1970) bystander intervention model (i.e., interpreting a potential sexual assault situation as dangerous, taking responsibility for intervening, deciding on an effective action, and intervening) and examining moderators of the associations between intoxication and these steps of bystander intervention. The project involves carefully developed novel, sophisticated, multi-method strategies that will maximize internal and external validity of the experiments. Study 1 is a laboratory-based experiment consisting of 128 young adults randomly assigned to receive an alcoholic [peak blood alcohol concentration (BAC) = 0.08%; n = 64] or a nonalcoholic control (n = 64) beverage after completing background questionnaires. Following the presentation of a sexual assault story, quantitative and qualitative data will be collected via interview to assess bystander intervention steps. Study 2 increases the ecological validity of our proposal by recruiting participants in a naturalistic setting and including a wider range of participant intoxication levels compared to the more controlled Study 1. In Study 2, 300 young adults who have been patronizing drinking establishments will report demographics, listen to and read one of four randomly assigned sexual assault stories in which the perpetrator and victim intoxication levels are varied (n = 75 per condition), complete brief self-report measures assessing the steps of bystander intervention, and take a BAC breath test. Findings will aid in understanding what factors contribute to sexual assault bystander intervention when consuming alcohol as well as how bystander intoxication should be addressed in sexual assault prevention programming. By understanding how, for whom, and in which situations alcohol influences bystander intervention for each bystander intervention model step and intoxication level, results will be used to increase the effectiveness of bystander intervention programming and reduce alcohol-related sexual violence. Together, findings will help to achieve our long-term goal of reducing alcohol-related sexual violence, fully consistent with NIAAA objectives as well as the goals of the White House Task Force on sexual violence and Healthy People 2020 of reducing alcohol-related violence and sexual aggression.